to asprimary and secondary types,are formed
(diplanetism)(Fig.3.11q). Dick (2001a) argued
that these two zoospore types should be desig-
natedauxiliaryandprincipaltypes, but this
terminology has not been widely adopted.
These zoospores in turn give rise toprimary
andsecondary cysts(Fig.3.11q) (Beakes 1983 ;
Holloway and Heath1977a,b; Sparrow 1960 ). In
many genera, however, the first zoospore gener-
ation is suppressed, giving rise directly toapla-
nospores(equivalent toprimary cysts), which
may be retained within the sporangium or dis-
charged. Molecular studies revealed that the
large genus Achlya was paraphyletic (Inaba
and Tokumasu 2002 ; Spencer et al. 2002 ), and
Spencer et al. ( 2002 ) proposed transferring
those species with centric or subcentric oos-
pores to a new genus,Newbya(Figs.3.10and
3.11n), leaving the remainder with eccentric
oospores in the genusAchlyas. str. (Figs.3.10
and3.11b). A summary of morphological char-
acteristics that might be used to resolve taxo-
nomic relationships within this order is given in
Fig.3.10, which was adapted from the unpub-
lished study that was briefly reported by Inaba
and Tokumasu ( 2002 ). We propose placing
those genera with predominantly single-
oospored oogonia and stronglyeccentric oos-
poresin a new family, the “Achlyaceae”. Those
genera and species with predominantly multi-
oospored oogonia andcentricorsubcentric oos-
poresare retained in theSaprolegniaceaes. str.a) Verrucalvaceae
Dick et al. ( 1984 ) erected the familyVerrucal-
vaceaeto include a newly described pathogen,
Verrucalvus flavofaciens(Fig.3.9k), the causal
agent of a yellowing disease of the turf grass
Pennisetum clandistinum(Kikuyu yellows), to
which they also controversially allied the gra-
minicolous downy mildew (GDM) genusScler-
ophthora. Subsequently, a soil-borne pathogen
of sugar cane (Saccharumspp.) roots,Pachy-
metra chaunorhiza (Fig. 3.9j), was also
included in this family (Dick et al. 1988 ). Sepa-
rately, on the basis of SSU rRNA sequence data,
Dick et al. ( 1999 ) created a new family, the
Leptolegniaceae, for a clade that included the
generaAphanomyces,Leptolegnia,andPlectos-
pira. In their final taxonomic synthesis they
placed bothPachymetra and Verrucalvusin
the order Sclerosporales, along with the GDMFig. 3.10 Simplified LSU rRNA tree of members of
Saprolegnialestogether with summary of some key
morphological characters (sporogenesis and mature
oospore cytology) associated with each clade. Unpub-
lished illustration from Inaba and Tokumasu ( 2002 )62 G.W. Beakes et al.